Assessment of kidney function : Creatinine is not the whole story

Abstract

Chronic renal insufficiency has ahigh prevalence and leads not only to a severe impairment in the quality of life but also to a higher mortality, mainly due to cardiovascular complications; however, in the early stages where there is still a chance for a therapeutic intervention, it is often underestimated because depending on endogenous factors (e.g. age and muscle mass), serum creatinine could falsely remain in the normal range while kidney function is already impaired. An exact measurement of the glomerular filtration rate (GFR) using radionuclide techniques is cumbersome and usually confined to rare cases, such as in clinical studies. Creatinine clearance measurement by 24-h urine collection requires good patient instructions and is error prone, thus it is limited to special circumstances. In routine clinical practice, estimation of the GFR by calculation algorithms provides the best approach. In recent years the chronic kidney disease epidemiology collaboration (CKD-EPI) formula has become established as the most accurate method. This should be used for screening and continuous surveillance. In addition, urinalysis including dipstick tests and urinary microscopy represent non-invasive, technically simple and economic screening tools. Due to its semiquantitative nature, the results of urinalysis should only to be interpreted after comprehensive consideration of the diagnostic and technical limitations, which are reviewed in this article.